The present invention relates to a thermosensitive recording adhesive sheet capable of forming colored images thereon upon application of heat, which comprises: (a) a support material with print patterns on the front side or back side on the support material, (b) a thermosensitive coloring layer formed thereon, (c) an adhesive layer formed on the back side of the support material, opposite to the thermosensitive coloring layer, and (d) a disposable backing sheet which is attached to the adhesive layer and can be peeled off the adhesive layer when the thermosensitive recording adhesive label is used. When necessary, a protective layer can be formed on the thermosensitive coloring layer for protecting the thermosensitive coloring layer from intrusion of adverse materials which may discolor the thermosensitive coloring layer and for improving the thermal head matching properties of the thermosensitive coloring layer during thermal printing by use of a thermal head or pen. Further, an undercoat layer can be interposed between the support material and the thermosensitive coloring layer by coating the layer on the support material in such a manner that the undulations of the support material are completely covered to form a smooth base for the thermosensitive coloring layer. This undercoat layer also serves to block the penetration of the components of the thermosensitive coloring layer into the support material, thereby protecting the thermosensitive coloring layer. Furthermore, a back coat layer can be formed on the back side of the support material, opposite to the undercoat layer, in such a manner that a print pattern is printed on the back coat layer, instead of directly printing a print pattern on the back side of the support material. This back coat layer is for preventing intrusion of the ink of the print pattern into the thermosensitive coloring layer, when the thermosensitive recording adhesive sheet comes into contact with water or organic solvents.
A conventional thermosensitive recording material comprises a support material made of, for example, a sheet of ordinary paper or synthetic paper, or a resin film, and a thermosensitive coloring layer, formed on the support material, on which coloring layer colored images can be formed by application of heat thereto. For application of heat for such image formation, for example, a thermal printer provided with a thermal head, a thermal pen and infrared rays are in general use.
Because of the capability of forming colored images by simple application of heat, such thermosensitive recording materials are widely used, not only for copying books and documents, but also for recording output information from computers, facsimile apparatus, telex and other information transmission and measuring instruments. Furthermore, such thermosensitive recording materials are employed as railway tickets and as adhesive labels for the POS (point of sales) system in supermarkets and department stores.
A thermosensitive recording adhesive sheet is such a sheet that allows thermal printing of images, characters or design patterns thereon, which can be stuck to any solid articles, with elimination of a disposable backing sheet from an adhesive layer formed on the back side of the thermosensitive recording adhesive sheet. Therefore, it is used as a variety of labels such as number plate label, price mark label, reagent label, name plate label and seal.
Generally it is desired that various designs, lines and characters be printed on such thermosensitive recording adhesive sheet prior to thermal printing. Conventionally, when such preprinting is desired, the desired designs, patterns or characters are printed on the top layer, for instance, on the thermosensitive coloring layer or on the protective layer, using a printing ink. However, when a thermal head comes into contact with the preprinted designs, patterns or characters in the course of thermal printing by use of a thermal head or pen, the components coming from the printed patterns or characters adhere or stick to the thermal head. As a result, tailing of the thermally printed images occurs and the thermal head matching properties of the thermosensitive recording material are considerably impaired.